Karyotyping
A CellServ PowerPoint Instructional Program
by
Mark S. Nardone
&
Roland M. Nardone, Ph.D.
Foundation for Advanced Education in the Sciences, Inc.
At the National Institutes of Health
Bethesda, MD
Karyotyping
Source: National Human Genome Research Institute
Karyotyping Defined
• Morphological characterization of chromosomes
• Description of the size and shapes of a diploid set
of chromosomes
• A photomicrograph of a set of chromosomes
arranged according to a standard classification
approach thereby providing the viewer with an
image of the sizes and shapes of all the
chromosomes
Human Karyotype (male)
Karyotyping serves many areas
of basic biology and medicine,
including
• Species Identification
• Gene Mapping
• Genetic Disease Analysis
Species Identification:
Each species has a characteristic
karyotype.
Human
Mouse
Banded Chromosomes are Used for Gene Mapping
Comparative Mapping: Human and Mouse
Chromosome 18
Many inherited diseases arise
from numerical or structural
chromosome aberrations.
Chromosome abnormalities are responsible for more
than 60 identifiable syndromes.
Cancer: 43 types
About 150 non-random chromosome
changes involving all chromosomes
except Y chromosome.
Cri du Chat Syndrome
(Microcephaly, retardation, etc.)
Deletion of short arm of chromosome 5
Fragile X Syndrome
Fragile site on long arm of X
chromosome
Down Syndrome
(Dysmorphic features: mental
retardation)
3 copies of chromosome 21
Human karyotypes are often used
as part of prenatal or postnatal
medical diagnoses.
Cell Cycle Map - Interphase
No chromosomes evident
Nuclear membrane intact
Nucleolus visible
DNA synthesis map:
G1- no DNA synthesis
S - DNA and chromosome
reduplication occur
G2 - Second discontinuity:
no DNA synthesis
Interphase lasts 95% of
cell cycle time
Cell Cycle Map: Stages of Mitosis
• Prophase: Onset of prophase
is marked by chromosome
condensation making
reduplicated chromosomes
visible.
• Metaphase: Chromosome
alignment in middle of cell
during metaphase; chromosome
condensation is maximal.
• Anaphase: Separation of
sister chromatids of
reduplicated chromosomes and
their migration to opposite
ends of cell; chromosome
decondensation begins.
• Telophase: Decondensation
continues. Nuclear
membranes begin to form
around the two sets of
chromosomes at opposite
poles.
• Cytokinesis - the
pinching in of the
cytoplasm to divide the
cell into two daughter
cells. May begin in
telophase.
Karyotyping – The Process
• Cell Culture Phase
• Cell Treatment Phase
• Slide Preparation Phase
• Preparation of Karyotype
Preparation of Chromosome Spreads for Karyotyping
Metaphase Blockade: log phase mammalian cell culture in
colchicine (0.06 mg/ml) for 3-4 hours
CMF-PBS Rinse; Detach Cells with Trypsin
Rinse, Pellet Cells by Centrifugation
Swell Cells with Hypotonic (0.075M) KCl; Pellet
Fix with Methanol: Glacial Acetic Acid (3:1)
Stain
Search for Ideal Chromosome Spread
Cell Culture Phase
Growth of mammalian cells in culture
Cell Cultures: A Crucial Component
• Provides a ready supply of cells in mitosis
• Can be manipulated to increase frequency of
cells in metaphase
• Can be manipulated to enhance the degree of
chromosome spreading. This allows for easier
counting, identification of chromosomes and
recognition of structural aberrations
• Lends itself to cytological examination;
chromosomes can be stained with a variety of
stains for different purposes
A Normal Mouse Embryo Cell Culture
Sources of Cultured Cells for Karyotyping.
Source
Purpose
Lymphocytes from peripheral blood
Clinical Diagnosis
Cultured fibroblasts collected by
amniocentesis or chorionic villus
sampling
Prenatal
Diagnosis
Established cell lines from human or
rodent:
IMR 90 Human Lung Fibroblast
Chinese Hamster Ovary Cells
T3 Mouse Prostate Cells
Research
Metaphase Blockade
1. Objective - to increase the number of cells in
metaphase.
2. Colchicine or colcemid is used to block cells
from going from metaphase to anaphase.
3. Drug inhibits assembly of microtubules needed
for mitotic spindle formation and movement of
chromosomes. Hence cells accumulate in
metaphase.
Hypotonic Treatment of
Metaphase Blocked Cells
1. Hypotonic salt solution (0.075M
KCl).
2. Causes cell swelling, cells are
more fragile, rupture easily when
splattered onto slides.
Fixation of Cells
• Carnoy's Fixative - 3 parts methyl alcohol to
1 part glacial acetic acid - almost
universally is the fixative of choice for
chromosome structural studies
• The fixative is freshly prepared immediately
before use
Application of Fixed Cells to Slide
1. Dispense cell suspension, dropwise, from a
fine bore pipette onto a clean slide.
2. The pipette tip should be several inches to 12
inches above the slide.
3. The slide may be flat on the table or propped
up at a 45O angle.
4. Allow slide to air dry.
5. Spreading of chromosomes is enhanced by the
evaporation of the fixative.
Staining Slides of
Chromosome Spreads
• Solid staining (non-banding) with giemsa stain is
the most common stain for routine preparations,
such as for chromosome counting.
• Such staining is not infallible for precise
identification of some chromosomes of similar
size and/or centromere localization. Among those
that may be misidentified because of size and
shape similarities are chromosomes 4 and 5, 10,
11, and 12, and 21 and 22.
• Typically, solid staining entails fixation with
methanol: glacial acetic acid (3:1), air drying,
staining with giemsa, rinsing, air drying and if
desired, mounting with permount.
Search for Ideal Chromosome Spread
No overlapping chromosomes
Chromosomes easily counted
Position of centromere is evident
Arms of reduplicated chromosomes readily
visualized
Make photographs of chromosome spread
Human Chromosome Spread
Preparation of Idiogram
Examine Ideal Chromosome Spreads (400X - 1000X)
Photograph
Enlarge Print
Cut out Chromosomes
Arrange Homologous Pairs
Assign Chromosome Numbers Based on Chromosome Size
and Centromere Position
Rearrange as Needed
Chromosome Identification
The centromere area is the primary constriction.
The arm above the centromere is designated as the p arm
and the one below the centromere is designated as the q
arm.
Identification is based on chromosome length and
position of the centromere. Chromosomes are
Metacentric (centromere in middle), Submetacentric
(centromere is slightly off center), Acrocentric
(centromere is far off center), Telocentric (centromere is
at end of chromosome)
.
Chromosome Classification
Metacentric
Subcentric
Acrocentric
Telocentric
Classification of Human
Chromosomes
Metacentric
1, 3, 16, 19, 20
Submetacentric
2, 4, 5, 6, 7, 8, 9, 10, 11, 12, 17,
18, X
Acrocentric
13, 14, 15, 21, 22, Y
Telocentric
No Telocentric Human
Chromosomes
HeLa – A human cancer cell. View shows three degrees of chromosome condensation.
Degree of condensation of metaphase chromosomes varies with the amount of time the
metaphase cell has been in colchicine
Satellites
• A chromatin mass of the short arm of a
chromosome; formed by a secondary constriction.
• The thin stalk of chromatin connection between the
satellite and the rest of the p arm contains the genes
for ribosomal RNA.
• Acrocentric chromosomes 13, 14, 15, 21 and 22
have satellites.
Structure of a reduplicated acrocentric
chromosome showing the primary
(centromere) and secondary (stalk/satellite)
constrictions
Chromosome Banding
• Eliminates any ambiguity in chromosome
identification
• Defined bands appear darker or lighter when
stained by Q, G, R and C banding methods
• Allows further scientific analysis in gene
mapping, identification of fragile sights, structural
changes such as translocations, and comparative
chromosome analysis
Photograph of G Banded Human Chromosome
Banding Techniques
•
•
•
•
Q (quinocrine fluorescent) banding
G (giemsa) banding
R (reverse) banding
C (centromere) banding
Summary
Karyotyping has several important roles in biology and
medicine ranging from gene mapping, to species identification, to
clinical diagnosis, to evaluation of potentially harmful chemicals in
the environment.
Key improvements in technique have contributed to its
usefulness. These include the use of proliferating cell cultures, the
enrichment of the frequency of metaphase cells by metaphase
blockade, the separation of chromosomes and swelling of cells with
a hypotonic solution and development of banding techniques which
assist in an accurate identification of the chromosomes and in
resolving structural Aberrations.